Due to the accumulation of heavy metal compounds produced by the sintering process in steel industry, the catalysts used for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) might be seriously deactivated. In this work, the deactivation effect of PbCl2, Pb(NO3)2, and PbSO4 on Mn-Ce activated carbon supported catalyst for low-temperature NH3-SCR of NO was investigated and compared. Poisoned catalysts were provided by impregnating fresh catalysts with Pb(NO3)2, PbSO4 and PbCl2 aqueous solutions, respectively. Deactivation could be observed on the poisoned samples, and the deactivation degree was following PbCl2 > PbSO4 > Pb(NO3)2. The catalytic activities of all samples were tested, and the physicochemical properties of fresh and poisoned catalysts were assessed. PbCl2 caused the most severe deactivation of the catalyst, owing to its poor redox property and surface acidity. Cl- could also react with Mn active sites to form -O-Mn-Cl bonds, resulting in additional acid sites, although these newly generated sites were not reactive in NH3-SCR reaction process. PbSO4 exhibited moderate poisoning effect due to the addition of SO42-, which created new Brønsted acid sites, facilitating the NH3 adsorption and NO reduction. Pb(NO3)2 had the least poisoning impact on the catalyst due to the NO3-, promoting the NH3 activation. The in situ DRIFTS results revealed that NH3-SCR reaction over all samples was governed by Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanism, and did not change due to the lead poisoning. Finally, a possible mechanistic model for different lead salts poisoning over Mn-Ce/AC catalyst was proposed.
Keywords: Acid sites; Deactivation; Lead salts; Redox ability; SCR catalysts.
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